A nano air vehicle (NAV) is commonly defined as an air vehicle with a maximum dimension of 7.5 centimeters in any axis, weighing 10 grams or less, and capable of at least 20 minutes endurance and 1-kilometer range.
At this scale, the aerodynamics and power are significant challenges. Multiple tradeoffs are involved. One approach to the challenges is to use lithium polymer batteries as part of the airframe. However, these tend to change size as they are used, impacting structure integrity. Another challenge is motor integration. Conventional fossil or battery powered motors are driven through gear mechanisms to turn a propeller or turbine. These designs impose severe range penalties, have a high specific mass fraction of total air vehicle, and endurance limitations which impact the overall ability to perform specific missions.
Propulsion of micro air vehicle (MAV) and NAV aircraft is traditionally affected through a conventional motor. The problem is that a motor, either electrical (usually DC) or fossil fueled, occupies a rather large portion of the vehicle mass fraction. Furthermore, as the MAV/NAV vehicle becomes more structurally efficient, the percentage devoted to propulsion utilizing conventional technologies increases further, implying an even harsher penalty in terms of payload due to propulsion requirements. Another significant drawback to conventional propulsion technology is implicit in the range capability of the vehicles. As the vehicles shrink in size, the ability to carry fuel, either electrical or fossil based, enforces strict limits on overall endurance. Thus, a vehicle which is capable of flight at just 30 knots is typically only capable of ranges 7-10 nautical miles. While this may be suitable for some applications, under true operational constraints, a significant increase in range is required in order to make the technology truly valuable to the user community.
Endurance is another area requiring improvement for MAV/NAV devices. Present technological limits are in the 30 minute range as evident by the AeroVironment® Black Widow design, typical of high performance MAV's. The flight duration under optimal conditions significantly limits utility to the operator. AeroVironment is a registered trademark of the AeroVironment Inc. Corporation of California.
Radioisotope power systems (RPS) are employed in spacecraft. Radioisotope thermoelectric generators (RTGs) have been used to power, for example, pacemakers and spacecraft, but are complex, requiring the source material, a walled container, thermocouples, and a heat sink to generate electricity. Nor is the energy produced by these compatible with the mass and volume constraints of MAV/NAVs.
What is needed, therefore, are techniques for an actuator for micro-scale vehicles that is efficient in power conversion, providing sufficient power to generate lift and thrust at this small scale of flight.